Drag and lift forces acting on a spherical bubble in a linear shear flow

The effects of fluid shear on drag and lift forces acting on a spherical bubble are studied for high particle Reynolds numbers of 0.5⩽Rep⩽200 by means of a three-dimensional numerical simulation, and the effects are compared with those for a solid particle. The results show that the fluid shear increases the drag acting on a bubble. On the other hand, the lift always acts from the lower fluid-velocity side to the higher fluid-velocity side, and tends to approach a constant value for high particle Reynolds numbers. Further, the asymptotic value of the lift increases with increasing fluid shear rate. Although the trend of the drag on a bubble against the fluid shear is similar to that on a solid particle, the trend of the lift is quite different. For a solid particle the direction of the lift changes from the higher fluid-velocity side to the lower fluid-velocity side with the increasing particle Reynolds number. The difference in the lift between a bubble and a solid particle can well be explained by taking account of pressure and viscous contributions to the lift.